Mud Dump Disposal Site Study - Background Information

frequency relationships (with error band estimates) for a particular disposal

mound configuration.

Detailed descriptions of how each of the above tasks of an erosion frequency

study should be conducted follow some background information on the Mud

Dump case study example.

Mud Dump Disposal Site Study - Background

Information

The frequency-of-occurrence methods described are illustrated in their appli-

cation to concerns over erosion of capped mounds at the Mud Dump disposal

site, the designated dredged material open-water disposal site for the Port of

New York and New Jersey (PNY/NJ). Critical to the management of dredged

material removed from the PNY/NJ is the remaining capacity within the Mud

Dump site. The above procedures were developed to assist in determining the

minimum water depths in which capped mounds can be placed without experi-

encing unacceptable amounts of erosion and therefore directly influence the ulti-

mate capacity of the Mud Dump site to contain contaminated dredged material.

At the time this appendix was written (1996), the Mud Dump disposal site

was virtually the only authorized site for open-water placement of dredged

material from the PNY/NJ. The site is a 1.12 by 2 n mile rectangle located

approximately 6 n miles east of Sandy Hook, NJ (Figure G2), in an area known

as the New York Bight. Water depths at the site range from less than 50 ft to

over 90 ft. As of October 1994, up to 65 M yd3 of dredged material (based on

scow logs) had been placed in the site. Because the Mud Dump site was the only

available disposal site for fine-grained dredged material from the PNY/NJ, the

remaining capacity was an extremely important issue in the overall plan for

managing dredging and disposal for the Port. Because of the large volume of

contaminated material inside the port, the remaining capacity of the Mud Dump

site for Category II (requiring special handling, i.e., capping for open-water

placement) dredged material (USACE/USEPA 1991) was critical in the sediment

management process for the New York District and the PNY/NJ.

At the request of the New York District, the U.S. Army Engineer Waterways

Experiment Station's Coastal Engineering Research Center (CERC) conducted a

study to define Mud Dump site capacity and other issues related to capping

(Clausner, Scheffner, and Allison 1995). Studies to compute the vertical erosion

frequency for mounds of various elevations in the Mud Dump site were the most

critical part of this effort. Previous studies have shown erosion of fine-grained

materials from mound flanks as a result of severe northeasters (McDowell 1993;

McDowell, May, and Pabst 1994). At the request of the New York District,

mounds with cap elevations ranging from 50 to 75 ft were modeled, with

ambient depths of 60 to 83 ft.

Appendix G Procedures for Conducting Frequency-of-Erosion Studies